Abstract: A Study of Gravity Anomalies of Bombay Offshore Structural High and Adjoining Area, India

Rai, D. and Ramaswamy, V. - Oil & Natural Gas Corporation Limited, India

Bombay High is a giant oil field in the platform area of Bombay Offshore Basin, which is situated on a divergent margin setup at the Western Continental shelf of India. Recently acquired gravity data of western offshore shows a major and broad gravity low anomaly over the positive structure of Bombay High. This gravity anomaly is unique in size, shape and character in the entire western continental shelf. In contrast with this Bombay High Gravity.

Low, the nearby Bombay coastal zone exhibits a prominent gravity high anomaly in an overall low gravity environment. Existence of two such anomalous features of opposite nature separated by a distance of 160 km only is intriguing and suggests a stressed and weak nature of the lithosphere in the region.

In this paper, we present a detailed gravity picture of the Bombay area comprising both offshore and onland. A profile passing through the anomalous features has been interpreted and a plausible geological model which would account for the observed gravity anomaly has been brought out. The model indicates a thick basalt column as a probable causative for the Bombay high gravity low. Heat-flow computations reveal that the Moho should have a temperature of about 675 deg. C, somewhat in excess of the Curie point of magnetites. The obvious inference from this finds support in the observed magnetic data. A model of underplating at the Moho level is also put forward as an alternate explanation for the offshore gravity anomaly.

AAPG Search and Discovery Article #90933©1998 ABGP/AAPG International Conference and Exhibition, Rio de Janeiro, Brazil